The federal agency sent warning letters to eight companies that sell chelation treatments online. The companies were told to immediately stop selling the products.

"These are in fact unapproved drugs," Michael Levy, director of the FDA's division of new drugs and labeling compliance, said at a news conference. "These companies falsely claimed that these drugs treat a variety of ailments, including autism and heart disease."

Chelation is a technique for treating people who have been poisoned with heavy metals such as lead, mercury, iron, and arsenic. Approved chelation drugs are available only by prescription and should be administered only by trained health professionals.

Several of the companies cited today by the FDA promoted their chelation products as treatments for autism and other chronic diseases.

"Unapproved chelation products are dangerously misleading because they target patients and the caregivers of patients with untreatable conditions," Levy said.

FDA medical officer Charles Lee, MD, noted that chelation can have serious side effects, particularly when people use the drugs or give them to children without medical supervision.

"Chelation can be dangerous and cause serious harm," Lee said at the news conference. "Chelation can result in dehydration, kidney failure, and even death. … People may also forgo useful medical treatments to use these products."

But Lee admits that the FDA does not really know what is in the "chelation" products sold over the counter, who is using them, or whether anyone has actually been injured by them. Today's action is based on the FDA's determination that the chelation products are being marketed as treatments for specific diseases -- in other words, as unapproved drugs.

Chelation has become a controversial alternative treatment for autism. FDA-approved chelation products are not approved for this use. However, some doctors -- despite no proof that it works and some evidence of harm -- use chelation to treat children with autism. Today's FDA action does not affect this off-label use of approved chelation products.

But that disclaimer doesn't satisfy Sallie Bernard. Bernard is president of the group SafeMinds, which maintains that mercury and other toxins cause autism in sensitive individuals. She says the FDA is implying that parents who get chelation for their children with autism are engaged in "wild practices."